This study is designed to determine the potential of BCG preparations to prevent the development of primary bronchogenic carcinoma in Syrian golden hamsters. Results indicate that BCG cell walls when administered after carcinogen exposure (BP-Fe2O3) significantly reduced lung tumor incidence from 75% in control animals to 50% in treated animals. Additional studies concerning the effect of BCG on alveolar macrophage tumoricidal capacity have shown that three distinct activation states can be identified. Macrophages from BCG immune-rechallenged hamsters are capable of destroying tumor cells while macrophages from BCG immune or normal hamsters do not. The tumoricidal capacity has been correlated to the response to chemotactic stimuli. Other functional parameters are being assessed to more closely identify characteristics of normal, activated-nontumoricidal and tumoricidal macrophages.